Biological systems use nanomachines, in that proteins are nanometers in size. The smallest component of a protein (the amino acid) is 3-10 angstrom or 1/3 to 1 nanometer. The largest enzyme complex can be 100 nanometers in diameter. In contrast, E.coli is several micrometers across - 10 times larger than its largest components - and is therefore a micromachine.

So much for biology. What about man made devices? Well, for a start, they will have to work in concert. In swarms and in co-operating groups. Each nanomachine can do one simple thing (bind a drug, compute a logical step in a calculation, act as a switch) and will have to interact with its fellow machines to complete a task.

Doesn't this defeat the purpose of having very small machines, if you have to have lots of them to do anything? Well, there are several advantages:

The last one is the most important for swarms that bridge the micro/meso/macro gap. Large scale objects (books, doors, clothing, furniture etc) that are composed of tiny, separate components are very much like living things. Adaptable, robust and programmable - they can be what you want them to be. Hopefully. :-)